1. Field of the Invention
The present invention relates to a pulse wave obtaining apparatus which obtains a cuff volumetric pulse wave produced in a cuff worn on a limb of a living subject, or a pressure pulse wave produced in an artery of a living subject, and a pulse wave analyzing apparatus which analyzes a cuff volumetric pulse wave or a pressure pulse wave.
2. Related Art Statement
A cuff pulse wave as pressure oscillation produced in a cuff (i.e., an inflatable bag) wound around a limb of a living person, in synchronism with heartbeat of the subject, is known as one of a plurality of sorts of information related to person's circulatory organ. Since this pressure oscillation represents the change of volume of blood in person's tissues, including arteries, around which the cuff is wound, it is called a cuff volumetric pulse wave. In addition, a pressure pulse wave as pressure pulsation produced in an artery of a person, in synchronism with heartbeat of the person, is also known as another sort of circulatory organ-related information. Information contained by the cuff volumetric pulse wave or the pressure pulse wave is analyzed to evaluate the circulatory organ or make a diagnosis on the same. For example, Patent Document 1 (International Patent Application Publication WO 88-04910 or its corresponding U.S. Pat. No. 5,099,853) teaches that a maximum magnitude of a heartbeat synchronous pulse of a pulse wave is used to estimate a systolic blood pressure of a person; Patent Document 2 (Japanese Patent Publication No. 2000-33078 or its corresponding U.S. Pat. No. 6,527,725) teaches that respective rising points of respective heartbeat synchronous pulses of respective pulse waves obtained from two different regions of a person are used to obtain pulse wave propagation velocity-related information representing arteriosclerosis of the person, and that the wave propagation velocity-related information and, optionally, a pulse area ratio and a pulse period are used to estimate a blood pressure (e.g., a systolic blood pressure) of the person; Patent Document 3 (Japanese Patent Publication No. 11-318838 or its corresponding U.S. Pat. No. 6,036,651) teaches that a pulse area ratio VR as the ratio of pulse area to pulse period is used to evaluate the blood outputting function of the heart of a person; Patent Document 4 (Japanese Patent Publication No. 7-275214 or its corresponding U.S. Pat. No. 6,413,224) teaches that a waveform characteristic value such as a pulse amplitude, a maximum slope SLOPE of a rising portion of a pulse, a pulse sharpness % MAP as the ratio of height position of gravity center of pulse area to pulse amplitude, a rising-portion percentage value as the ratio of rising-portion time to pulse period, and a peak index PI as the ratio of time between maximum point to next peak point to pulse period is used to determine an estimated blood pressure of a person; an augmentation index AI as the ratio of amplitude of reflected wave to amplitude of incident wave is used to indicate arteriosclerosis of a person; Patent Document 5 (Japanese Patent Publication No. 5-200030) teaches that a blood pressure ratio as the ratio of maximum magnitude of a pulse after change of posture to maximum magnitude of a pulse before the change of posture is used to indicate autonomic imbalance; and Patent Document 6 (Japanese Patent Publication No. 9-215664 or its corresponding U.S. Pat. No. 5,830,148) teaches that fluctuations of respective maximum magnitudes of respective heartbeat synchronous pulses that are iteratively determined are used to indicate activity of autonomic nerve.
Meanwhile, the cuff volumetric pulse wave is obtained by extracting, from an electric signal representing the cuff pressure detected by a pressure sensor connected to a cuff via, e.g., a rubber tube, an oscillatory component representing the pulse wave, using a band-pass filter. Therefore, when the pulse wave propagates through air in the cuff or the rubber tube that has a great compliance, the waveform of the pulse wave is distorted. Thus, the extracted cuff volumetric pulse wave may not be sufficiently accurate, and the evaluation of person's circulatory organ and/or the diagnosis made on the same based on the pulse wave may not be sufficiently accurate, either. In addition, in the case where the cuff volumetric pulse wave is used, on the assumption that it represents the change of intra-arterial pressure, to evaluate the circulatory organ or make diagnosis on the same, the waveform of the pulse wave is additionally distorted by the skin and/or subcutaneous tissue of the person, and the above-indicated problem is worsened.